Preferably, medical dairy products are highly concentrated in nutrients, in particular in proteins and minerals, to meet the daily intake of nutrients in malnourished patients. These patients can be cachectic patients or persons suffering from end-stage AIDS or cancer, or in cancer treatment, suffering from severe pulmonary diseases like COPD (chronic obstructive pulmonary disease), tuberculosis and other infection diseases, or persons that experienced severe surgery or trauma, such as burns. Furthermore, persons suffering from disorders in the throat or mouth such as oesophageal cancer or stomatitis and persons having problems with swallowing like dysphagic persons, require special liquid, low-volume concentrated liquid or semi-liquid nutrition. Also, persons just suffering from reduced appetite or loss of taste, will benefit from low-volume, preferably liquid, food. These patients can also be elderly persons, in particular frail elderly and elderly at risk of becoming frail. In this regard, although an elderly person's energy needs may be reduced, their ability to consume products may also be diminished. For example, they may have difficulty consuming a product due to, e.g., swallowing difficulties, or due to too large amount of product they need to consume to meet the daily intake of nutrients. Hence, compliance is not optimal, and often, the intake is suboptimal, leading to suboptimal nourishment, and in the end, to malnutrition. Other persons who may be interested in consuming such nutritional compositions may be healthy persons such as a sportsman or sportswoman or an active elderly, who are in need of a concentrated nutrition in a small volume, such as the low-volume liquid enteral nutritional composition according to the invention with a high content of nutrients, in particular proteins.
All aforementioned groups of patients may be extremely sensitive to food consistency and to the organoleptic properties of the product such as, for instance viscosity, mouth feel, taste, smell and colour. Also, patients such as cachectic patients, typically suffer from extreme weakness which often prevents them from sitting in a vertical position and from drinking food from a carton or even to suck it from a straw. These patients benefit well from low-volume liquid enteral nutritional compositions with a high content of nutrients, in particular proteins.
However, high amounts of protein and minerals increase the overall viscosity of the product during processing, in particular during a heat treatment such as sterilization at ultra-high temperature, so as to remain stable for at least nine months at ambient temperature, or pasteurization, and storage because of shifts in the protein-mineral equilibria. Low viscous liquid products, however, are mostly appreciated by patients, which makes it challenging to formulate such products. Also, a low viscosity is required for a nutritional composition being suitable for tube administration.
Therefore, the problem underlying the present invention is to provide an enteral liquid nutritional composition, either as a supplement, or as a complete nutrition, comprising a high amount of an intact protein, in particular micellar casein, as major protein source, in the smallest volume of liquid, having a low viscosity after heat treatment, and which supports nutrition and well-being in the different patient groups mentioned above, in particular to an elderly person, a person that is in a disease state, a person that is recovering from a disease state, a person that is malnourished, or a healthy person such as a sportsman or sportswoman or an active elderly.
A further problem is to provide a process for the heat treatment of a enteral liquid nutritional composition comprising a high amount of an intact protein, in particular micellar casein, during which treatment the viscosity of said composition does not increase, or not significantly increase, such that a heat treatment process can be used in a larger time/temperature window, i.e. for a longer time and/or at a higher temperature than currently available in the art.
A further problem is to provide an enteral liquid nutritional composition comprising a high amount of an intact protein, in particular micellar casein, with a high heat stability, in particular measured as heat coagulation time.
Casein micelles, as can be found in micellar casein, are remarkably stable against heat. Their stability is maintained by hydrophobic and electrostatic interactions, colloidal calcium phosphate (CCP), and steric effects of protruding chains of κ-casein. Nevertheless, physical and chemical changes occur in the casein micelles during heating of milk due to shifts in the salt equilibria. Heating induces aggregation, which is the first step to instability. This is often reversible. However, subsequently the aggregates may coagulate, thus forming irreversible aggregates, also called coagulates. The changes in salt equilibria become partly irreversible with heating above 120° C., such as with sterilization at ultra-high temperature; they include alterations in structure and composition of the original micellar calcium phosphate into a more insoluble form. Other irreversible changes that occur during heating are hydrolysis of phosphoserine residues, degradation of lactose, and release of κ-casein from the micelle.
Upon heating, coagulation becomes visible when large aggregates have emerged or when a gel is formed. In the art, the resistance of milk, in particular milk protein, against coagulation during heating is called heat stability. The time needed for coagulation is called the ‘heat coagulation time’, abbreviated HCT (Walstra, P., Wouters, J. T. M., & Geurts, T. J. (2006) Dairy science and technology Boc Raton, USA: CRC press). The HCT of milk is highly dependent on pH, as pH affects the protein charge, the amount of CCP in the micelle, and the concentration of free calcium ions in the serum phase. Moreover, the HCT is influenced by the type of milk, because the HCT as function of pH is considerably different for Type A and B milk. The HCT of concentrated milk (7.0-9.0 weight % protein) is much lower than for non-concentrated milk.
The heat stability of (concentrated) milk can be manipulated by addition of calcium chelators, as it is known to affect the concentration of free calcium ions and thereby the integrity of the micellar structure. Phosphates and citrates are commonly used in the dairy industry as heat stabilizers. Orthophosphate and citrate produce a slightly different increase in heat stability because of precipitation of calcium orthophosphate complexes on the micelles and precipitation of calcium citrate complexes in the serum phase. Polyphosphates, such as sodium hexametaphosphate and sodium phytate, increase the heat stability of milk by binding to positively charged amino acids of the casein micelle. Calcium chelators might also, at high chelator concentration, decrease the heat stability of a milk system, as they can chelate a critical level of CCP from the casein micelle at which the integrity of the micellar structure is lost.
The heat stability of normal milk, concentrated milk, evaporated milk, and artificial casein micelle systems has been extensively studied. However, to our knowledge, no studies have systematically evaluated the heat stability of commercial concentrated micellar casein solutions (MCI) at pasteurization or sterilization conditions, for example for a retort sterilization for 20 minutes at 270° C., and for a number of phosphate-based heat stabilizers. An advantage of using micellar casein solutions, such as prepared from MCI powder, instead of concentrated milk is that it contains a small to negligible amount of whey protein. Moreover, although there is general consensus that phosphates and citrate enhance heat stability of milk systems, it is known that the effectiveness with which they do this, differs considerably depending on the source of protein applied.
Unpublished PCT/NL2011/050168 discloses the use of one or more chelating agents selected from the group consisting of a phosphoric acid, citric acid, a soluble phosphate salt, a soluble citrate salt, or a mixture thereof, for independently controlling the viscosity and the transparency of an aqueous micellar casein composition comprising 6 to 20 g/100 ml of micellar casein, and having a pH of about 6 to 8. Heat stability is not addressed.